Snail infestation has been a problem for some time at waste water treatment facilities. The snails grow and reproduce prolifically in the trickling filter towers and/or nitrification towers of these facilities, and are then carried to the bioflocculation tanks where they accumulate. Snail accumulations of depths up to four feet have been observed in all channels of the bioflocculation tanks. As the snail shells are pulverized they pass into the secondary clarifiers degrading the quality of the effluent. Eventually, the shells get into the digesters and contribute to grit buildup. Waste water treatment systems have problems with the snails grazing on nitrifying bacteria, that is, eating the microbiological fauna. This fauna provides secondary treatment of suspended solids (SS) and reduces biochemical oxygen demand (BOD); elimination of this fauna, therefore, interferes with the nitrification process and causes the effluent to be in violation of discharge permits.
An example of a particular snail that is a problem is one that belongs to the genus Physa or Physella. These organisms are freshwater snails that need a moist environment and can live submerged. These snails are hermaphroditic and capable of self-fertilization. They lay egg cases once or twice per year and die after spawning is completed. Their normal life span is one year. There is about a three week incubation period before juvenile snails appear. Juveniles go directly from the egg to the adult morphology; there is no snail egg larvae stage.
It is known that dialkyl diallyl ammonium polymers, alone or in combination, will kill zebra mussels and larvae in submerged water intake systems as disclosed in U.S. Pat. Nos. 5,015,395; 5,062,967; and 5,096,601, the disclosures of which are incorporated herein in their entirety by reference. Use of these or similar compounds, however, has not been reported in the killing and control of snails in general, or in waste water treatment systems in particular; nor has use of the compound been reported against any other organisms that do not have a larvae stage.
The polymers used in the present methods are used in municipal and industrial water treatment. For example, dimethyl diallyl ammonium chloride polymers are added as clarification aids to the water intakes of municipal potable water plants. To the best of the inventors' knowledge, however, such polymers have not been added to control snail growth or fouling.
Additionally, polyquaternary compounds have been utilized for control of other organisms, such as Asian claims (Corbicula) and microorganisms such as bacteria, fungi, and algae in aqueous systems. See, for example, U.S. Pat. Nos. 4,462,914; 4,113,709 and 4,111,679. Simple quaternary ammonium compounds have been used to control fouling of microorganisms and molluscs. See, for example, Nashimura et al., Japan Kokai No. 74 81,535 (1974); Roth, German Offenlegungsschrift No. 2,642,606; Sindery, French Pat. No. 1,460,037 and McMahon et al., presentation at American Power Conference, Chicago, Apr. 23-25 (1990).
Ramsey et al., "Effects of Nonoxidizing Biocides on adult Corbicula fluminea" (1988), disclose the use of various biocides, including dodecylguanidine hydrochloride (DGH), benzalkonium chloride, pyridinium chloride, dioctyl dimethyl ammonium chloride, poly[oxyethylene(dimethylamino)-ethylene (dimethylamino)-ethylene dichloride], glutaraldehyde, 2,2-dibromo-3-nitrilo propionamide, N4-dihydroxy-.alpha.-oxobenzene ethanimidoyl chloride, 5-chloro-2-methyl-4-isothiazolin-3-one/2-methyl-4-isothiazolin-3-one, N-[(.alpha.)-(1-nitroethyl) benzyl] ethylenediamine and 2-(tert-butylamino)4-chloro-6(ethylamine)-5-triazine, to control Asian clams.
U.S. Pat. No. 4,816,163, to Lyons et al., discloses the use of water-soluble alkyl guanidine salts, alone or in combination with methylene bis-thiocyanate or alkyl dimethyl benzyl ammonium chloride, to control the biofouling of macroinvertebrates, particularly Corbicula.
None of the above patents or articles appear to disclose the methods of the present invention.
Current treatment to reduce snail populations is pH adjustment, which is detrimental to the biological organisms in the secondaries. There remains a need, therefore, for methods for controlling snails without affecting the organisms which reduce BOD in the secondary treatment process.